The horn fly, Hematobia irritans (L.), is a persistent pest of pastured cattle and costs the cattle industry an estimated $730-876 million annually. When horn flies are abundant, cattle suffer from annoyance and blood loss, and alter their grazing habits. Behavioral changes may be manifested by decreased milk production, reduced weight gains and poor feeding efficiency. Horn fly densities of several hundred flies per animal are common among uncontrolled populations. Proposed economic thresholds for horn flies on cattle vary from 50 to 230 per animal; however, 200 flies per animal is the generally accepted standard.
The management of horn flies has traditionally relied on the use of insecticides applied as dusts, sprays, pour-on, boluses and feed activities, and insecticide impregnated ear tags. Pyrethroid ear tags were highly effective against the horn fly and densities below 50 flies per head were relatively easy to maintain until the development of resistance. Resistance is now widespread throughout most of North America and control has become increasingly difficult.
Pyrethroid resistance was suspected in the horn fly population associated with the dairy herd at the Center for Environmental Farming Systems (CEFS), located at Goldsboro, N.C. Traditionally, these cattle were treated with pyrethroid insecticides to manage the horn fly population. In spring 2000, pour-on pyrethroid insecticides were applied every 2 weeks to the milking cows. Despite this treatment, horn fly populations exceeded 200 flies per animal. Attempts to manage the horn fly population on the CEFS dairy herd using conventional pyrethroid insecticides was ineffective and an alternative to this method was needed. Changing formulations or active ingredients would be expected to reduce horn fly densities and improve production. However, certain insecticides are restricted from use on lactating dairy cattle. Furthermore, at least one research group found alternative insecticide treatments (organophosphate class) were not able to reduce fly densities to less than 50 flies per head, nor did the use of insecticides affect weight gains. The group surmised that the elimination of the horn fly was not possible in Florida and perhaps management around a 200 fly threshold was an attainable objective with added benefits to resistance management and reduced pesticide use.
Using multiple strategies for the management of pests and reduction of pesticides is the foundation of integrated pest management (IPM). Trapping insects may contribute significantly to the IPM program. An early attempt at trapping insects involved the use of a walk-through horn fly trap. This passive device, with subsequent modifications, was designed to brush flies from the animals and capture them in baffles until they died. Some researchers recognized that some horn flies momentarily left the host when cattle entered darkened fly traps thus avoiding capture. They modified the trap design with a translucent skin to increase ambient light with the trap resulting in fewer flies leaving the hosts before entering the trap.
As horn fly populations and other insect populations become increasingly difficult to control with insecticides, improved technology for removing such insects from livestock is desirable, especially for dairies. Further, it is desirable to provide effective and low-maintenance technology for removing insects from livestock without the use of insecticides.